Coating compositions often include solid colorant and/or filler particles dispersed in a resinous binder system to impart color and/or performance properties in the resulting coating. Such particles tend to have a strong affinity for each other and, unless separated by, for example, some other material, tend to clump together to form agglomerates. Therefore, dispersants are often used in coating compositions. A dispersant is a substance that provides repulsion forces to counteract particle-particle attraction. Dispersants are often polymers that contain segments that adsorb to a particle surface and other segments that build loops or tails that provide steric stabilization.
Pigments and fillers used in coating compositions often consist of solid particles having a primary particle size of about 0.02 to 2 microns (i.e., 20 to 2000 nanometers). “Nanoparticulate” pigments and filler materials usually have an average primary particle size of 300 nanometers or less, sometimes 100 nanometers or less. Agglomeration is a serious problem for nanoparticulate pigments and filler materials because they have a relatively large surface area. Thus, acceptable dispersion of such nanoparticulates can often require an inordinate amount of conventional dispersant to effect de-agglomeration and to prevent subsequent re-agglomeration.
The presence of such high levels of dispersant, however, in the final coating composition can be detrimental to the resultant coating. For example, high levels of dispersants have been known to contribute to water sensitivity of a coating and to negatively impact the durability, hardness, and/or scratch resistance of such coatings.
As a result, it would be desirable to provide dispersions of nanoparticles wherein the dispersant can be used at reduced levels as compared to prior art dispersants. Such dispersions can, in at least some cases, allow for particle incorporation into coatings as desired, without negatively impacting film properties.